Not quite true. While non-citizens can join the military, they must first come to the United States and be a legal permanent resident and the military cannot and will not assist in that immigration process. However, there are special expedited naturalization procedures for those who do serve in the military in a time of war or for their spouses for those who die while serving honorably for active duty military. There are also expedited naturalization procedures for people who marry U.S. citizens, but again, you don't just get citizenship by marrying a U.S. citizen. You still must emigrate to here, become a permanent legal resident, and live here for at least three years (it's five if you don't marry a U.S. citizen).

Short answer - it is strictly necessary for you to emigrate. The only exception would be if you are already a citizen through jus sanguinis or jus soli.

"You need something to make it knownThat it's you and no one else that ownsThat spot that yer standing, that space that you're sittingThat the world ain't got you beatThat it ain't got you lickedIt can't get you crazy no matter how manyTimes you might get kickedYou need something special all rightYou need something special to give you hopeBut hope's just a wordThat maybe you said or maybe you heardOn some windy corner 'round a wide-angled curve"

As an American, let me assure you that in our hearts you are American in spirit. I say this because you are all American in spirit, we just haven't assimiliated you all yet. But we'll get to it someday.